The present invention is directed to golf balls, and in particular, to restricted flight (or limited flight) golf balls. The golf balls of the present invention are designed to travel a distance that is shorter than the distance travelled by standard golf balls. This is accomplished through the use of an inefficient dimple pattern and/or elastomeric compositions having reduced coefficient of restitution (C.O.R.) values in comparison with balls constructed of conventional elastomeric blends. The balls are durable, have good click and feel characteristics, and with the exception of exhibiting the restricted or limited flight performance, have performance characteristics comparable to that of conventional golf balls.
Restricted flight golf balls are desirable for a number of reasons. For instance, they are less likely to be hit over a driving range retaining wall or fence. This factor alone increases the safety of those who are located just outside the retaining wall, and also assists in preventing the balls from becoming lost. Also, more compact driving ranges and golf courses can be developed in areas of high real estate values and/or high population densities.
In reducing the distance a golf ball will travel when hit, there are a variety of factors which are to be considered. The coefficient of restitution, along with ball size, weight and additional factors such as club head speed, angle of trajectory, and ball aerodynamics (i.e., dimple pattern), generally determine the distance a ball will travel when hit. Since club head speed and the angle of trajectory are not factors easily controllable, particularly by golf ball manufacturers, the factors of concern among manufacturers are the coefficient of restitution and the surface dimple pattern of the ball.
A golf ball's coefficient of restitution (C.O.R.) is the ratio of the relative velocity of the ball after direct impact to that before impact. One way to measure the coefficient of restitution is to propel a ball at a given speed against a hard massive surface, and measure its incoming velocity and outgoing velocity. The coefficient of restitution is defined as the ratio of the outgoing velocity to incoming velocity of a rebounding ball and is expressed as a decimal. As a result, the coefficient of restitution can vary from zero to one, with one being equivalent to an elastic collision and zero being equivalent to an inelastic collision.
The coefficient of restitution of a one-piece golf ball is a function of the ball's composition. In a two-piece or a multi-layered golf ball, the coefficient of restitution is a function of the core, the cover and any additional layer. While there are no United States Golf Association (U.S.G.A.) limitations on the coefficient of restitution values of a golf ball, the U.S.G.A. requires that the golf ball cannot exceed an initial velocity of 250 .+-./-5 feet/second. As a result, golf ball manufacturers generally seek to maximize the coefficient of restitution of a ball without violating the velocity limitation.
The present invention is directed to the production of restricted or limited flight golf balls through the use of inefficient dimple patterns and/or low coefficient of restitution elastomer compositions. No U.S.G.A. limitations exist in regard to the minimal coefficient of restitution and/or velocity of a golf ball, particularly for driving range balls and/or practice balls, the specific subject matter of the present invention.
In this regard, it has been found by the inventors that by reducing the coefficient of restitution of a standard traditional flight golf ball from around 0.800 to around 0.560, about a 50 yard reduction in carrying distance can be achieved. Such a low C.O.R., however, is generally undesirable because it causes the ball to feel too "dead" when hit. It has also been found that the projection or lift of such a low C.O.R. ball cannot be greatly enhanced even with the incorporation with specialty design dimple patterns. As a result, such low C.O.R. balls do not exhibit the playability characteristics of a conventional golf ball.
Certain competitive one piece restricted flight range balls exist exhibiting reduced PGA compression. Whereas top grade golf balls are 100 PGA compression, these prior art restricted flight range balls are 60 PGA compression (i.e. approximately 0.095 in Riehle compression). However, these low compression balls feel soft or "mushy" and do not have desired click or feel exhibited by the present invention. See, for example ball "D" in Example 1 below. Also, these balls have C.O.R. values of around 0.685, which is greater than the C.O.R.'s of the present invention, and as such do not provide a sufficiently limited distance.
Another more established method for decreasing the distance travelled by a golf ball is to reduce the ball's weight. See, for example, U.S. Pat. No. 4,839,116. In this regard, golf balls having micro-balloons or microscopic glass bubbles inside the core component of the balls to reduce weight are known in the art. However, weight reduction, as with reducing the coefficient of restitution to the above-described low values, is undesirable. If a ball with a given dimple pattern is too light in weight, it will fly too high in trajectory. Also, the ball's feel, as well as its wind stability, are adversely affected.
Moreover, reducing a ball's weight increases the cost of manufacturing the ball in that the standard inexpensive heavy mineral fillers are used to a lesser extent or not at all. Thus, such light weight balls are not particularly desirable.
One object of the present invention is to provide novel and improved elastomeric cores or centers useful for the construction of solid one-piece or multi-layered golf balls having lower coefficient of restitution values. Another object is to provide golf balls which, because of their core or center composition, exhibit reduced driving distance without sacrificing desirable playability aspects of the golf balls, such as compression, weight and feel, upon club head impact. The overall performance characteristics of the balls of the invention are, with the exception of the restricted flight characteristics, essentially the same as conventional golf balls.
An additional object of the present invention is to develop a golf ball that is approximately 45-50 yards shorter in total distance off a driver than the longest range ball sold by Spalding & Evenflo Companies, Inc. (i.e. Spalding's "Super Range") without affecting the balls size, weight or compression. This is accomplished by combining an inefficient dimple pattern with elastomeric compositions C.O.R. values of about 0.560 to about 0.670, with C.O.R. values for the core compositions of multi-layered restrictive flight golf balls of about 0.560-0.640 being more preferred).
Specifically, the reduction in C.O.R. values has been achieved by the development of an elastomeric compositions which, when utilized in the construction of one-piece golf balls or supplemented with resinous cover stock formulations and/or additional core components for the construction of multi-layered balls, and configured with an inefficient dimple pattern, form restricted flight driving range golf balls that have trajectories similar to that of conventional golf balls.
These and other objects and features of the present invention will become more apparent upon a reading of the following summary and description of the invention and from the claims.